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class SceneDelegate {
   var navigationController: UINavigationController!
 ...
    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
      guard let sceneWindow = (scene as? UIWindowScene) else { return }
      window = UIWindow(windowScene: sceneWindow)
      window?.makeKeyAndVisible()
      navigationController = UINavigationController(rootViewController: makeRootViewController())
      window?.rootViewController = navigationController
    }

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class ViewControllerA { 
  var onButtonTappedObserve: (() -> Void)?
  ...
  @IBAction func buttonTapped(_ sender: UIButton) {
      onButtonTappedObserve?(// dependencies if any)
  }
  ...
}

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protocol DatabaseManagement {
  func insert(_ articles: [Article], completion: @escaping (Result<Bool, Error>) -> Void)
  func retrieve(completion: @escaping (Result<[Article], Error>) -> Void)
  func delete(_ article: Article, completion: @escaping (Result<Bool, Error>) -> Void)
}

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GET *url*

200 RESPONSE

{
	"items": [
		{
			"id": "a UUID",
      			"title": "a title",
			"description": "a description",

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struct FeedItem {
  let id: UUID
  let title: String
  let thumbnailURL: URL
  let description: String?
  let createdDate: Date
}

struct RemoteFeedItem {
  let id: UUID

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struct User {
  var id: UUID
  var accessToken: String?
  var username: String?
  var imageURL: URL?
  var email: String?
  var address: String?
}

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class FeedViewModel {}

class FeedViewController: UIViewController {
  
  private var viewModel: FeedViewModel?
    
    init(viewModel: FeedViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
    }

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class FeedViewModel {}

class FeedViewController: UIViewController {
  
  private var viewModel: FeedViewModel?
  
  override func viewDidLoad(){
    super.viewDidLoad()
    viewModel = FeedViewModel()
  }

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class AllCategoriesViewController: UIViewController {
  
  var loader: FeedLoader?
 
  func viewDidLoad(){
    super.viewDidLoad()
    
    loadFeed()
  }
  

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protocol FeedLoader {
  func load(completion: @escaping ([FeedItem]) -> Void)
}